A very annoying problem for a great many number of users is having to switch between various different “public” smtp servers as they move between their office network, home adsl and their 3G connections. The common solution around this is to either use an authenticated relay system via some host or tools such as winroute. No longer.
Expanding on the technology we’ve used for the last few years to provide a split zone for .dyndns.uls.co.za with differing IPs for local (within ZA) and international (outside ZA) we’re now able to provide alternative CNAME records depending on which network you’re requesting resolution of smtp.uls.co.za from. What this means is that if you’re using the SAIX network then resolving smtp.uls.co.za will result in a CNAME for smtp.saix.net, which will then give you the appropriate SMTP server for that network (The expansion of the core technology to deal with more than ZA vs Intl was due to the fact that there is no longer peering between SAIX and MWeb – so at least something good has come from that).
Currently supported networks is listed below:
SAIX: smtp.saix.net
Internet Solutions: smtp.isdsl.net
MWeb: smtp.mweb.co.za
Vodacom: smtp.vodacom.co.za
Cell C: smtp.cellc.co.za (doesn’t properly resolve, see below)
MTN: smtp.mtn.co.za (untested)
iBurst: smtp.iburst.co.za
Note that smtp.cellc.co.za resolves to a CNAME for smtp.uunet.co.za which then fails to resolve – non-authoritatively, which is even worse than a NXDOMAIN result.
Note that in many cases this is still not good enough as many networks, for example IS Business DSL, doesn’t provide a static relay you can use. Nor can we reliably differentiate between these users on the same network (eg, we can’t differentiate between IS Business DSL and normal IS DSL) due to the way that routing on the Internet and name resolution functions. In these cases you probably have a hosted exchange/imap setup anyway, or your on-site IT support deals with this for you. If you bump into a network where this does NOT work for you, please browse to http://www.whatismyip.com/ and send us your IP address, and if possible information regarding the ISP that is being used (we can probably deduce this from the IP address) to support@uls.co.za.
Tags: smtp
Hi
I’m with Nashua
ip
196.30.245.149
We’re using:
relay.nashuaisp.co.za
but also get redirected to:
smtp.mtnbusiness.co.za
When that is down.
Hi Frans,
MTN and MTN Business seems to use the same ASN number, as such it’s very difficult (impossible) for me to distinguish between those users that should be using smtp.mtn.co.za and those that should be using smtp.mtnbusiness.co.za (relay.nasuahisp.co.za is a simple CNAME for smtp.mtnbusiness.co.za). I’ll sleep a bit on this but it may require more fine-grained per-subnet overrides. Potentially do-able.
Kind Regards,
Jaco
We’ve tracked down and resolved a problem specific to iBurst. Whilst previous reports indicated that iBurst was working we now believe those reports to have been faulty. We have gained access to an iBurst connection and have confirmed that it should be sorted out and fixed now.
WebAfrica’s SMTP = smtp.wa.co.za
For example, my current IP address on my ADSL connection is: 41.185.75.24 -> dsl-185-75-24.dynamic.wa.co.za
Some added notes:
I think the correct Vodacom SMTP is smtp.vodamail.co.za and the correct MTN SMTP is mail.mtn.co.za
Thank you for this excellent idea! Very clever indeed.
Thanks Chris!
I’ve added smtp.wa.co.za but cannot test as I don’t have a WA account. I’ve only picked up one ASN number for them so hopefully that is sufficient.
smtp.vodacom.co.za and smtp.vodamail.co.za resolves to the same IP address – so I’m going to leave it at smtp.vodacom.co.za for the moment.
Can someone with an MTN connection possibly confirm?
Hi Jaco
Do I have your permission to create a CNAME record to your smtp.uls.co.za hostname? For example:
smtp.mydomain.co.za. IN CNAME smtp.uls.co.za.
Are you planning to continue running this service in the future or is it a temporary thing?
I would like to offer this SMTP server solution to my friends/family that use multiple ISPs for their connectivity…
Hi Chris,
You’re welcome to. We introduced the service because we were tired of having to figure out exactly which ISP some our clients were using, and it’s annoying to have to keep switching SMTP servers ourselves. We don’t plan on abandoning the service unless we are being forced to do so due to legal issues and or complaints from the Tier-1 ISPs. At this stage this seems unlikely and we’ve even had requests similar to your own from some of the larger ISPs in South Africa.
The common solution is to provide clients with an authenticated relay, but then some ISPs like iBurst go and block outbound smtp connections. It’s possible to use ports other than 25 but explaining how to configure this over the phone is often hard. Turns out it’s far easier to just detect the network the person is on by using the BGP routing tables and ASN lookups for the DNS servers (s)he is using. Only two known breakages currently, and that’s for people that use the opendns or google name servers. So listen up folks: For the sake of DNS response times and for us being able to track which ISP you’re resolving from – use the DNS servers assigned by your ISP.
Hi Jaco
That’s excellent – thank you very much!
Could you perhaps create a page to let us know for which SMTP servers (support networks) you provide relaying?
Thanks again, keep up the good work.
And by the way, I think the correct SMTP relay server for Cell C users is:
smtp.cmobile.co.za
Afraid not.
Using domain server:
Name: 41.157.83.50
Address: 41.157.83.50#53
Aliases:
Host smtp.cmobile.co.za not found: 3(NXDOMAIN)
And with regards to the page listing supported networks – you’re looking at it. The intent is to update this blog entry as more entries becomes available.
At the moment only one problem network (as per above) is known, Nashua Mobile – which operates on IP space leased from Internet Solutions, and thus a lookup of the DNS servers results in the IS ASN being located and their SMTP servers being returned. That and the SMTP relay for Cell C … (I’m ON Cell C at the moment and I don’t know)
Interesting…
Thank you nonetheless!
Hi
For CellC give mail.cmobile.co.za a try.
220 mta-esher-2.cmobile.co.za ESMTP Sendmail 8.14.4/8.14.4; Sun, 18 Sep 2011 19:33:30 +0200
I think Esher refers to CellC’s office in Sandhurst, just off Rivonia Road, behind the Shell Garage
That looks good. Updated to mail.cmobile.co.za – so hopefully Cell C will now work too. I’ve also added records for datapro earlier today, but they are unconfirmed as of yet.
For Neotel: smtp.neomail.co.za
Added, please do test.
Very good idea .
Makes it easy. Just have to put in one smtp no matter ISP.
Sample transciption of a logged call to the ISP for an email problem.
Helpdesk agent : what is in your smtp address field.
User : smtp.uls.co.za.
Helpdesk agent : please key in smtp.{service provider}.co.za
User : But i dont want to & smtp.uls.co.za works
Helpdesk agent : but that is not our smtp server
User : smtp.uls.co.za resolves to the same adress as smtp.{service provider}.co.za.
Helpdesk agent: i cannot help you because that is not our server.
User : Agggh Sh$# + %^%$%^